Not Applicable
Not Applicable
Not Applicable
The present invention relates to sensing circuitry, and more particularly to circuitry, associated with flow sensor, that provides significantly faster response times as compared to circuitry in similar prior art sensors.
There exists a demand for a mass flow controller (MFC) having a step response of less than 300 mS. The flow indicator signal of a flow sensor operating in a constant current supplied bridge circuit has been shown to exhibit a time constant of about 3 seconds, so that it takes more than 8 seconds for the signal to be appreciably close to its final value. The flow indicator signal of a flow sensor operating in a constant temperature (of sensor) configuration has been shown to be much faster (about 50 mS), but characteristics of the indicator signal are affected by the ambient temperature. In brief, a MFC operating in a constant current mode is stable, but slower than desired. A MFC operating in a constant temperature mode can provide the desired step response, but provides a signal that may be biased by the ambient temperature.
In one aspect of the present invention, a flow pickup circuit for receiving a flow signal from a flow sensor and providing a flow indicator signal corresponding to flow characteristics through the flow sensor comprises an inner bridge circuit, an outer bridge circuit, and a processor. The inner bridge circuit is constructed and arranged so as to operate in a constant current mode, and to produce a first sensing signal. One or more of the components of the inner bridge is the flow sensor. The outer bridge circuit is constructed and arranged so as to operate in a constant temperature mode, and to produce a second sensing signal. The inner bridge circuit is one of the components of the outer bridge circuit. The processor receives the first sensing signal and the second sensing signal, and produces the flow indicator signal therefrom.
In another embodiment, the inner bridge circuit includes four components connected in a series loop characterized by a first pair of diagonally-situated nodes and a second pair of diagonally-situated nodes. The first sensing signal includes a voltage potential between the first pair of diagonally-situated nodes.
In another embodiment, two of the four components include the flow sensor, disposed between the second pair of diagonally-situated nodes.
In another embodiment, the outer bridge circuit includes four components connected in a series loop characterized by a first pair of diagonally-situated nodes and a second pair of diagonally-situated nodes. The second sensing signal includes a voltage potential between the first pair of diagonally-situated nodes.
In another embodiment, one of the four components includes the inner bridge circuit, disposed between the second pair of diagonally-situated nodes.
In another embodiment, the processor multiplies the first sensing signal by the second sensing signal so as to produce a product, and divides the product by a workpoint current value so as to produce a constant current flow indicator.
In another embodiment, the processor subtracts an ambient temperature component from the second sensing signal, so as to produce a constant temperature flow indicator.
In another embodiment, the ambient temperature component is generated by subtracting the second sensing signal from the first sensing signal so as to produce a difference signal, then passing the difference signal through a low-pass filter. The low-pass filter may include an analog filter (i.e., for filtering analog signals) known in the art, or a digital filter (e.g., FIR, IIR, etc.) known in the art.
Another embodiment further includes at least one scaling module for scaling at least one of the first sensing signal and the second sensing, so that the first sensing signal and the second sensing signal have compatible magnitudes.
Another aspect of the invention comprises a method of receiving a flow signal from a flow sensor and providing a flow indicator signal corresponding to flow characteristics through the flow sensor. The method comprises producing a first sensing signal via an inner bridge circuit, constructed and arranged so as to operate in a constant current mode, wherein one or more of the components of the inner bridge is the flow sensor. The method further includes producing a second sensing circuit via an outer bridge circuit, constructed and arranged so as to operate in a constant temperature mode, wherein the inner bridge circuit is one of the components of the outer bridge circuit. The method further includes receiving the first sensing signal and the second sensing signal and producing the flow indicator signal therefrom.
Another embodiment further includes producing the first sensing signal via the inner bridge circuit that includes four components connected in a series loop characterized by a first pair of diagonally-situated nodes and a second pair of diagonally-situated nodes. The first sensing signal includes a voltage potential between the first pair of diagonally-situated nodes.
Another embodiment further includes producing the second sensing signal via the outer bridge circuit that includes four components connected in a series loop characterized by a first pair of diagonally-situated nodes and a second pair of diagonally-situated nodes. The second sensing signal includes a voltage potential between the first pair of diagonally-situated nodes.
Another embodiment further includes multiplying the first sensing signal by the second sensing signal so as to produce a product, and dividing the product by a workpoint current value so as to produce a constant current flow indicator.
Another embodiment further includes subtracting an ambient temperature component from the second sensing signal, so as to produce a constant temperature flow indicator.
Another embodiment further includes generating the ambient temperature component is generated by subtracting the second sensing signal from the first sensing signal so as to produce a difference signal, and passing the difference signal through a low-pass filter.
Another embodiment further includes scaling at least one of the first sensing signal and the second sensing via at least one scaling module, so that the first sensing signal and the second sensing signal have compatible magnitudes.
In another aspect, the invention comprises a flow pickup circuit for receiving a flow signal from a flow sensor and providing a flow indicator signal corresponding to flow characteristics through the flow sensor. The flow pickup circuit includes an inner bridge circuit constructed and arranged so as to operate in a constant current mode, and to produce a first sensing signal. The inner bridge circuit includes four components connected in a series loop, characterized by a first pair of diagonally-situated nodes and a second pair of diagonally-situated nodes. The first sensing signal is given by a voltage potential between the first pair of diagonally-situated nodes. Two of the four components include the flow sensor, disposed between the second pair of diagonally-situated nodes. The flow pickup circuit further includes an outer bridge circuit, constructed and arranged so as to operate in a constant temperature mode, and to produce a second sensing signal. The outer bridge circuit includes four components connected in a series loop, characterized by a first pair of diagonally-situated nodes and a second pair of diagonally-situated nodes. The second sensing signal is given by a voltage potential between the first pair of diagonally-situated nodes, wherein one of the four components includes the inner bridge circuit. The flow pickup circuit also includes a processor for receiving the first sensing signal and the second sensing signal, and producing the flow indicator signal therefrom. The processor subtracts an ambient temperature component from the second sensing signal, so as to produce a constant temperature flow indicator.
In another aspect, the invention comprises a flow pickup circuit for receiving a flow signal from a flow sensor and providing a flow indicator signal corresponding to flow characteristics through the flow sensor. The flow pickup circuit includes means for producing a first sensing signal. The means for producing a first sensing signal includes the flow sensor and operates in a constant current mode. The flow pickup circuit also includes means for producing a second sensing signal that includes four components connected in a series loop characterized by a first pair of diagonally-situated nodes and a second pair of diagonally-situated nodes. The second sensing signal includes a voltage potential between the first pair of diagonally-situated nodes, and one of the four components includes the inner bridge circuit. The flow pickup circuit also includes means for receiving the first sensing signal and the second sensing signal, and for subtracting an ambient temperature component from the second sensing signal, so as to produce a constant temperature flow indicator. The ambient temperature component is generated by subtracting the second sensing signal from the first sensing signal to produce a difference signal, and passing the difference signal through a low-pass filter.